1. Preheat oven to 350. Grease 8x8 square baking dish.
2. Whisk together sugar, flour, and salt in a medium sized mixing bowl.
3. Whisk together egg yolks, flax milk, vanilla extract, lemon zest, lemon juice, and Greek yogurt in a separate mixing bowl.
4. Combine the egg mixture with the sugar mixture. Mix with a spoon.
5. Beat egg whites until stiff peaks form.
6. Gently fold the egg whites in to the mixture.
7. Pour into prepared baking dish and bake for 30 minutes or just until set.